iter_not_returning_iterator:

* Check HIR tree first.
* Check name by symbol.

Author: Jarcho

clippy_lints/src/iter_not_returning_iterator.rs

@@ -4,7 +4,7 @@ use rustc_hir::def_id::LocalDefId;
 use rustc_hir::{FnSig, ImplItem, ImplItemKind, Item, ItemKind, Node, TraitItem, TraitItemKind};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::declare_lint_pass;
-use rustc_span::symbol::sym;
+use rustc_span::{sym, Symbol};
 
 declare_clippy_lint! {
     /// ### What it does
@@ -43,30 +43,27 @@ declare_lint_pass!(IterNotReturningIterator => [ITER_NOT_RETURNING_ITERATOR]);
 
 impl<'tcx> LateLintPass<'tcx> for IterNotReturningIterator {
     fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'_>) {
-        let name = item.ident.name.as_str();
-        if matches!(name, "iter" | "iter_mut") {
-            if let TraitItemKind::Fn(fn_sig, _) = &item.kind {
-                check_sig(cx, name, fn_sig, item.owner_id.def_id);
-            }
+        if let TraitItemKind::Fn(fn_sig, _) = &item.kind
+            && matches!(item.ident.name, sym::iter | sym::iter_mut)
+        {
+            check_sig(cx, item.ident.name, fn_sig, item.owner_id.def_id);
         }
     }
 
     fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx ImplItem<'tcx>) {
-        let name = item.ident.name.as_str();
-        if matches!(name, "iter" | "iter_mut")
+        if let ImplItemKind::Fn(fn_sig, _) = &item.kind
+            && matches!(item.ident.name, sym::iter | sym::iter_mut)
             && !matches!(
                 cx.tcx.parent_hir_node(item.hir_id()),
                 Node::Item(Item { kind: ItemKind::Impl(i), .. }) if i.of_trait.is_some()
             )
         {
-            if let ImplItemKind::Fn(fn_sig, _) = &item.kind {
-                check_sig(cx, name, fn_sig, item.owner_id.def_id);
-            }
+            check_sig(cx, item.ident.name, fn_sig, item.owner_id.def_id);
         }
     }
 }
 
-fn check_sig(cx: &LateContext<'_>, name: &str, sig: &FnSig<'_>, fn_id: LocalDefId) {
+fn check_sig(cx: &LateContext<'_>, name: Symbol, sig: &FnSig<'_>, fn_id: LocalDefId) {
     if sig.decl.implicit_self.has_implicit_self() {
         let ret_ty = cx
             .tcx